We have focused in three related areas: 1. the study of vFLIP, a KSHV latent gene product expressed in KSHV-infected cell targets and in Kaposi's sarcoma (KS), Primary Effusion Lymphoma (PEL) and Multicentric Castleman's disease;2. the study of CXCR7, a G protein-coupled receptor induced by KSHV in the host cells, and its related receptor CXCR4, which is not induced by KSHV;and 3. the development of new therapies for KSHV-induced malignancies occurring in AIDS patients. One of the characteristic features of KSHV is its ability to infect endothelial cells,and to indirectly promote angiogenesis and lymphangiogenesis predominantly by promoting the recruitment of cells that produce pro-angiogenic factors and promoting the expression of pro-angiogenic genes by the cells it infects. ORFK13/vFLIP encodes a 188-amino acid protein, which binds to the Ikappab kinase (IKK) complex to activate NFkappaB. We examined ORFK13/vFLIP contribution to KS phenotype and potential for therapeutic targeting. To this end, we have retrovirally transduced ORFK13/vFLIP into primary human endothelial cells and examined the contribution of this gene to KS phenotype. We found that ORFK13/vFLIP induces the spindle morphology distinctive of KS cells and promotes formation of abnormal vascular networks typical of the disorderly KS vasculature. Microarray analysis of gene expression in endothelial cells transduced with ORFK13/vFLIP detected increased expression of pro-inflammatory cytokines, chemokines, and interferon-responsive genes. This study represents the first comprehensive analysis of gene regulation by KSHV-vFLIP. As one might expect from stimulation of pro-inflammatory cytokines and chemokines, we found that ORFK13/vFLIP stimulates adhesion of inflammatory cells characteristic of KS lesions. The microarray analysis found that ORFK13/vFLIP promotes the expression of thymidine phosphorylase, a cellular enzyme that can metabolize the prodrug 5-fluoro-5-deoxyuridine (5-dFUrd) to 5-fluouridine (5-FU). A potent thymidine synthase inhibitor, 5-Fu blocks DNA and RNA synthesis. When tested for cytotoxicity, 5-dFUrd (0.1-1muM) selectively killed ORFK13/vFLIP-expressing endothelial cells while sparing control cells. These results demonstrate that ORFK13/vFLIP directly and indirectly contributes to the inflammatory and vascular phenotype of KS, and identify 5-dFUrd as a potential new drug that targets KSHV latency for the treatment of KS and other KSHV-associated malignancies. In additional studies, we have found that the conditioned medium from K13/vFLIP-expressing endothelial cells induces STAT1 phosphorylation in control cells but not in U5A cells that are lacking the IFNalpha receptor beta subunit (Ifnar2) 190, suggesting that K13/vFLIP induces type-I interferon secretion to activate STAT1. By ELISA, we detected IFNbeta1 in the culture supernatants of endothelial cells only after K13/vFLIP was expressed. Thus,IFNbeta1 is at least one of the humoral factors induced by K13/vFLIP to stimulate STAT1, which could also explain why K13/vFLIP expression in endothelial cells promotes the transcription of a variety of IFN-inducible genes 189. Type I IFNs exert antiviral functions in virus-infected cells by inducing p21, initiating cell cycle arrest, and inhibiting viral replication. The IFN response usually represents an integral part of the hosts immune response against viruses and virus-infected cells. It is puzzling that KSHV has maintained during evolution this antiviral function of K13/vFLIP, which is potentially damaging to its persistence. We are now analyzing the potential significance of this observation and are testing the hypothesis that the IFN response induced by K13/vFLIP can block KSHV replication, thereby modulating viral replication. One of the cellular genes that are highly induced by KSHV is the chemokine receptor RDC1/CXCR7. Recent studies have shown that CXCR7 binds the chemokines SDF1 and I-TAC but it is still unclear whether CXCR7 can signal in response to these ligands or other signals, or whether its function is to serve to sequester ligands away from their receptors. Recently, CXCR7 was shown to oligomerize with CXCR4, a receptor that can signal in response to SDF1. We are interested in the function of CXCR7 in the context of KSHV infection. We have overexpressed or silenced CXCR7 in PEL (Primary Effusion Lymphoma) cell lines and tested their tumorigenicity in mice. Initial observations have shown that CXCR7 promotes PEL-induced tumor progression. We are currently exploring the mechanisms underlying this pro-tumorigenic effect of CXCR7 in the context of PEL malignancy. PEL is a fatal viral malignancy in humans, which typically presents as a malignant effusion that later disseminates. In spite of therapy with high-dose chemotherapy or other therapies, PEL is a rapidly fatal malignancy. Rapamycin, which targets mTOR (mammalian target of rapamycin), an effector of cell signaling pathways often deregulated in cancer, showed efficacy against a variety of tumors, particularly those of lymphoid origin. We have investigated the potential utility of Rapamycin for the treatment of experimental PEL. Previous studies have suggested that rapamycin could be effective against subcutaneous PEL in mice. However, this pre-clinical model is far removed from the disease in patients in its location and progression. Recently, PEL development in rapamycin-treated post-transplant recipients raised questions about the drug's anti-PEL activity. We have developed and used a murine model of effusion PEL progressing to peritoneal tumors to investigate the anti-PEL activity of rapamycin. We found that rapamycin significantly reduces ascites accumulation and extends mouse survival. Initially, rapamycin reduced PEL load compared to control mice, but most mice rapidly showed PEL progression. Levels of VEGF, which promotes vascular permeability contributing to effusion formation, were significantly reduced in ascites of rapamycin-treated mice compared to controls. Expression of IL-10, the principal autocrine growth factor for PEL, was initially reduced in PEL from rapamycin-treated mice but rapidly increased despite treatment. We found that the hypoxic environment of ascites and rapamycin cooperate in stimulating IL-10 expression in PEL. These results do not support the use of rapamycin as a curative treatment for PEL, but identify rapamycin an effective drug to reduce accumulation of malignant effusions. Current efforts in the laboratory are intended to further characterize development of PEL resistance to rapamycin and how to prevent it. In particular, we are testing the potential efficacy of combining rapamycin to neutralization of IL-10.